Add base64 encode/decode functions for IE 9

The audio player code for producing .m3u files in Javascript relies
on the window.btoa() function being available, but that's only
supported in IE 10. To ensure that IE 9 (and earlier, but it's 9
that we really care about) works properly, we'll need this shim.

Source: http://code.google.com/p/gflot/source/browse/trunk/flot/base64.js?r=153
License: "This library is free.  You can redistribute it and/or modify it."
New "audioplayer" directive works

This directive creates two icons for playing audio, one speaker icon
to play the audio, and a second one to download it. The "play the audio"
icon creates an .m3u file on-the-fly (without needing a server roundtrip)
and sends that file to the browser to be downloaded and processed with
whatever the user's default .m3u handler is. The .m3u contains nothing
but an absolute URL to the .mp3 file, so that the user's audio handler
will start downloading (and streaming) the .mp3 right away. Result: audio
playing that should be straightforward across all browsers and platforms
without needing to use the HTML5 audio tag.

This commit also contains test code for the directive, in the form of
a #/robintest URL. In the next commit that test code will be removed,
in preparation for merging into master.
Removed test code for audioplayer directive

This is now ready to be merged into master.